bridging the gap - AR15.COM

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Posted: 4/11/2016 1:31:19 PM EDT

so I have searched and read opinions but if you have a mount that bridges the gap. like a ADM, aero, or any other one piece mount.

if your reciever and free float rail are quality made how is this so called flex going to affect it? sounds more like its smoke blow.

but lets get a current debate not something 6 years ago thats flawed.

Posted: 4/11/2016 1:36:50 PM EDT

[#1]

The issue is with manufacturing tolerances between the rail, barrel nut and upper.
Any misalignment or variances in the contact faces of the rails will cause uneven clamping with the mount, and if it's not avery rigid mount it will transfer this to the scope.
If it IS a rigid mount, it will try to force the rail and upper into alignment which could cause other issues.

In reality, if you've bought quality components, you will likely never notice an issue.

Posted: 4/11/2016 1:42:57 PM EDT

[#2]

I'm more concerned about handguard flex when impacted and how this would transmit force back to the bridged mount. The handguard will be like a lever and the attachment point the fulcrum where movement will be like a crowbar or a claw hammer pulling out a nail.

There is also the issue of whether the handguard has anti-rotation tabs, how tightly they line up to the receiver, and how securely the handguard is attached. Some use small screws affixing it to the barrel nut. These might not keep the handguard from rotating or flexing.

While all of this is theoretical, equalizing the clamping forces of the mount and preventing flex or movement is best maintained by keeping the mount entirely on the upper rail slots. This is especially the case if the mount is intended to be a QD return to zero style.

Posted: 4/11/2016 2:21:55 PM EDT

[#3]

i guess if i dropped my weapon and bent the rail but that even would take exceptionaly force

Posted: 4/11/2016 3:37:41 PM EDT

[#4]

I guess you see in the photos that your rail and upper are not aligned. One is clearly higher than the other and not on the same plane. Whether there is a gap between the two is only one consideration. Think about what that is doing to the mount and its clamping forces. And that is now, without any external force being applied if it should be dropped or impacted or twisted.

Posted: 4/11/2016 3:43:07 PM EDT

[#5]

Unless the rails are perfectly aligned you'd get uneven contact with the mount. If it was the only option I had to run an optic where I wanted until I got the proper mount it wouldn't bother me.

Wouldn't expect any difference in precision, but accuracy may be off and have to re-zero if it was zereod to the receiver previously.

Also, I wouldn't expect the mount to return to zero as effectively because torquing the mount differently would cause the position of the forward rail to shift.

Posted: 4/11/2016 8:54:10 PM EDT

[#6]

I wouldn't unless it's a monolithic rail

Posted: 4/11/2016 9:27:16 PM EDT

[#7]

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Quoted:
I wouldn't unless it's a monolithic rail

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Posted: 4/13/2016 12:10:01 AM EDT

[#8]

for now until I can afford or trade into a recon-x I flipped it and have it mounted to the rail. since I shoot ntch

Posted: 4/13/2016 10:28:24 PM EDT

[#9]

What is "it" that you flipped? What mount and optic? You need to optimize eye relief and stay on tbe upper. Until you get an extended one piece mount you might want to extend your stock a notch and back your nose away a bit, if necessary. Got a pic of tbe mounted optic?

Posted: 4/14/2016 12:06:09 AM EDT

[#10]

Posted: 4/14/2016 8:04:00 AM EDT

[#11]

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Quoted:
http://i.imgur.com/FRhQRx2.jpg

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That handguard is a clamp-on, right? The only thing holding it is friction on the barrel nut from the two small clamp bolts on bottom.
I'm not sure what will happen when you put some rounds through it with ~3x the weight tugging on it...

Posted: 4/14/2016 9:43:24 AM EDT

[#12]

Thanks. I guess that "will do", temporarily, but pressure on the rail will change POI. Its the equivalent to not being free floated.

The scope will move in relation to the barrel when you apply pressure to the rail with a bipod or even in an adjustable front rest. Even a couple thousandths of an inch flex translates into several inches at the target.

Posted: 4/17/2016 9:20:30 PM EDT

[#13]

Why on earth would you not just put it on the receiver? Even with NTCH you don't have correct eye relief with that setup, tossing aside the 200 dollar mount designed to forward mount your scope so that you don't need to ignore the last ten years of Ar15/optics/mounting knowledge.

maybe an arms SIR or vltor casv would be better ha Stuart's if you want clip on with a Long top rail. Or a pri handguard and a swan sleeve.

Posted: 4/17/2016 10:27:44 PM EDT

[#14]

There are more than enough "extended" optic mount options out there nowadays that allow you to get the correct eye relief without bridging the upper/rail. It may cost a little bit of money, but it usually does when you try to do things the correct way instead of half-assing it.

As for the "anti-rotation" tabs on MI rails, they aren't exactly known for being bulletproof.

Posted: 4/18/2016 12:33:47 AM EDT

[#15]

Here is an example of what right looks like.

Posted: 4/18/2016 1:13:47 AM EDT

[#16]

well I should have went with a recon x. but right now I am just going to switch to a red dot probably or even use my irons. wanted to use my 10.5 for a little more range and how I set it up now it works fine

Posted: 4/18/2016 9:12:09 AM EDT

[#17]

Just take off that stupid bubble thing, flip the mount back around, and move the scope farther forward in the rings. Your sacrificing your whole setup around that bubble instead of the other way around.. Put the bubble on IF you still have room after you mount your scope in a decent position.

Posted: 4/18/2016 9:15:37 AM EDT

[#18]

Quote History

Quoted:
Just take off that stupid bubble thing, flip the mount back around, and move the scope farther forward in the rings. Your sacrificing your whole setup around that bubble instead of the other way around.. Put the bubble on IF you still have room after you mount your scope in a decent position.

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I concur with this, the bubble level will do nothing for you inside the effective range of your short barrel...

Posted: 4/18/2016 11:19:18 AM EDT

[#19]

Quote History

Quoted:
Just take off that stupid bubble thing, flip the mount back around, and move the scope farther forward in the rings. Your sacrificing your whole setup around that bubble instead of the other way around.. Put the bubble on IF you still have room after you mount your scope in a decent position.

View Quote

This.

You have a workable solution if you just make a few small changes. There really isn't any need to be NTCH either. That was simply to create a repeatable index point with irons.

It causes a ton of eye relief problems now because people hang onto the notion that it is correct.

Posted: 4/18/2016 7:09:42 PM EDT

[#20]

I shoot ntch so it does matter. but as of now I have it how I need it to work

Posted: 4/19/2016 8:16:03 PM EDT

[#21]

I don't know about you, but it requires an uncomfortably long LOP to give me a cheek weld further rearward than NTCH... like longer than an A2 stock... unless I'm purposefully pulling my neck back and leaving slack in it, which is bad shooting form.

Posted: 4/19/2016 8:29:43 PM EDT

[#22]

You don't think your handguard flexes? Grab the end of your handguard, take your thumb and apply some pressure to the barrel. Watch the barrel change position within the handguard. If you are using a sling, bipod, rest, etc you could be having that same kind of deflection.

Posted: 4/20/2016 2:54:40 AM EDT

[#23]

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Quoted:
I shoot ntch so it does matter. but as of now I have it how I need it to work

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So you come in here to ask questions, start a thread, and then when the answers you get don't agree with your preconceived ideas, you dismiss them and go about with your original thought process? Makes sense.

Posted: 4/20/2016 9:06:21 AM EDT

[#24]

Just put the mount back on the upper where it belongs and remove that long range bubble which serves no purpose with such a short, lower velocity barrel.

Push the scope fully forward within the mount using the extra space that bubble level was occupying. That should get you to NTCH or very close. At worse, you might have to slide your rear stock back one click.

If still not satisfied, get a more extended mount and sell your present one here on equipment exchange. With your present setup your POI will change with pressure on the rail, just as if it were not free floated.

People here are patiently trying to help you. Please listen to them.

Posted: 4/20/2016 9:07:49 AM EDT

[#25]

Quote History

Quoted:
Just putbthe mount back on the upper wbere it belongs and remove that long range bubble which serves no purpose with such a short, lower velocity barrel. Puch the scope fully fkrward within the mount using thecextra space that bubble kevel was occupying. That should get you to NTCH or very close. At worse, you might have to slide your rear stock back one click.

If not satisfied get a more extended mount and sell your present one here on equipment exchange. With your present setup your POI will change with pressure on tbe rail, just as if it were not free floated.

View Quote

You might want to slide back a click or two from that keyboard

Posted: 4/20/2016 10:03:45 AM EDT

[#26]

Quote History

Quoted:

I concur with this, the bubble level will do nothing for you inside the effective range of your short barrel...

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:
Just take off that stupid bubble thing, flip the mount back around, and move the scope farther forward in the rings. Your sacrificing your whole setup around that bubble instead of the other way around.. Put the bubble on IF you still have room after you mount your scope in a decent position.

I concur with this, the bubble level will do nothing for you inside the effective range of your short barrel...

Bubble levels aren't for use in short barrels or low powered optics. That level is just adding weight and taking up space.

Posted: 4/20/2016 10:49:47 AM EDT

[#27]

Quote History

Quoted:
http://i.imgur.com/FRhQRx2.jpg

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Reminds me of a rice rocket, jusssst a little bit. This thread delivered.

Posted: 4/20/2016 7:25:16 PM EDT

[#28]

LOL wow OP your shit is all retarded. Listen to everyone else here trying to help you. Flip that mount around and ditch the bubble. You'll be fine if you listen to good advice.

Posted: 4/20/2016 10:38:26 PM EDT

[#29]

Quote History

Quoted:

You might want to slide back a click or two from that keyboard

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:
Just putbthe mount back on the upper wbere it belongs and remove that long range bubble which serves no purpose with such a short, lower velocity barrel. Puch the scope fully fkrward within the mount using thecextra space that bubble kevel was occupying. That should get you to NTCH or very close. At worse, you might have to slide your rear stock back one click.

If not satisfied get a more extended mount and sell your present one here on equipment exchange. With your present setup your POI will change with pressure on tbe rail, just as if it were not free floated.

You might want to slide back a click or two from that keyboard

Lol. When typing on a mobile device you have to go back and edit, which I did as you were posting.

Posted: 4/20/2016 11:25:20 PM EDT

[#30]

have a mro now so I'm set

Posted: 4/21/2016 10:56:36 AM EDT

[#31]

Quoted:
so I have searched and read opinions but if you have a mount that bridges the gap. like a ADM, aero, or any other one piece mount.

if your reciever and free float rail are quality made how is this so called flex going to affect it? sounds more like its smoke blow.

but lets get a current debate not something 6 years ago thats flawed.

View Quote

Hanguards move in relation to the bore. Receiver rails don't.

You mount your scope fully on the receiver rail to eliminate a potential variable. I'm sure there are plenty of rifles and shooters where bridging the gap would not make a noticeable difference. However, if the scope shifts a millimeter, that's going to translate to a huge point of impact shift at 600 yards (or less). The people that shoot for precision at those kinds of distances are not going to take the chance that a bridge the gap mount might work out. Instead, they'll just buy what they need to mount their scope in a way that eliminates as many potential variables as possible. In fact, the vast majority of shooters make the same decision, regardless of whether they shoot at medium range or for precision.

I've had a bad scope mount on a .308 bolt gun. You really need to see a bad mount in action to understand how little movement at the mount it takes to throw off point of impact. Changing to a good mount took the rifle from 4-5 moa to 1. There was no movement in the mount that you could see or feel. However, each recoil would shift the scope ever so slightly. I shot up a lot of ammo before I figured out I needed a new mount.

I cut corners on lots of gun parts. I do not cut corners on scope mounts.

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